This invention relates to plunger-type utility locks which are highly pick resistant and which cannot be opened by existing keys, and to keys for the locks of this invention which also open many prior plunger-type locks.
Plunger-type utility locks, also sometimes referred to as barrel locks, are widely used by utility companies to prevent unauthorized access to meters, valves, connectors, etc. which control and measure the supply of utility services, such as electricity and gas. However, the locks are often defeated and the meters, valves, connectors, etc. tampered with to obtain utility services without charge. The problem is growing as the cost of utility services increases, because the higher costs result in a greater loss of revenue for each unit of service obtained without charge and the higher costs provide more incentive to obtain the services without charge.
In the most widely used plunger-type utility locks, the plunger has an axial opening of substantial length which receives a key adapted to open the lock. The plunger is spring biased away from the head of the lock and displaces locking balls radially outwardly beyond the shank of the lock to provide a locked condition. The typical key has fingers which are expanded to grip the plunger on the interior surface of its axial opening, and means for retracting the finger-gripped plunger to open the lock. Favored means of picking plunger-type locks include using a bent wire to hook the spring and pull it back to relieve the tension on the plunger, which can then fall to its open position, and jamming one or more nails or the like in the axial plunger opening and thereafter using the nail to retract the plunger and open the lock. A successful utility lock must resist these common means of picking.
However, the utility locks are not always opened by picking or other forceful means. Instead, they are often opened by or through the use of keys which have been lost by or stolen from the utility companies. Accordingly, any new utility lock will preferably resist being opened by existing keys. It will be understood that a utility company will not replace all of its locks at one time for reasons of economics, and it is desirable that the key for any new utility lock be capable of opening existing prior locks so that personnel will not have to carry more than one key. Utility companies also prefer to have a lock and key system which is not shared with other neighbor companies, so that a key lost by one utility company cannot be used to open locks of another utility company.
The distribution of keys can be further limited if the locks are designed to be supplied in their open condition and closed to their locked position without the use of the usual key. Thus, personnel merely installing locks do not need to be provided with a key.
It is also important that any new utility lock conform to the size and shape which has become standard throughout the various utility companies, so that receptacles for the locks and other equipment utilizing the locks to secure meters, valves, connectors, etc. can accept the new locks without alteration.